Rf signal generating device

ABSTRACT

Apparatus for generating an RF signal for use in RF signal detection is described. The apparatus comprises at least one processor configured to generate a set of IQ data based on at least one set of weighted IQ data, each set of weighted IQ data having a respective weight and a circuit configured to generate an RF signal using the set of IQ data. The at least one processor is configured to calculate each respective weight in dependence upon location of a signal detector or an antenna associated with the RF signal detector.

FIELD OF THE INVENTION

The present invention relates to a device for generating an RF signalfor use in RF signal detection. In particular, the device can be usedfor training operators of RF signal detection equipment.

BACKGROUND

Devices which can detect and measure radio frequency (RF) signals can beused in a variety of different applications including spectrummanagement and security. For example, RF signal detection equipmenthaving a direction finding capability can be used to identify and locateRF sources (herein referred to as “RF transmitters”).

Operators (or “users”) need to be trained to use such types of devices.However, there are considerable challenges to providing these users witheffective field training. For instance, RF sources need to be deployedand configured, and be operated in a controlled manner. This may beonerous, time consuming and/or complex, particularly if sources aremobile and frequencies need to be coordinated. Moreover, it may benecessary to procure a licence to operate sources which may be costly toobtain and/or which might place tight restrictions on operation. In somecases, licences may be unavailable.

SUMMARY

According to a first aspect of the present invention there is providedapparatus comprising at least one processor configured to generate a setof IQ data based on at least one set of weighted IQ data, the or eachset of weighted IQ data having a respective weight, and a circuitconfigured to generate an RF signal using the set of IQ data. The atleast one processor is configured to calculate each respective weight independence upon location of an RF signal detector or an antennaassociated with the RF signal detector. The location may be an actuallocation or a simulated location. The location of the apparatus may beused as the location.

Each set of weighted IQ data can be used to generate data for simulatinga respective wireless RF transmitter. However, the RF signal can besupplied to an RF signal detector by a wired connection. Thus, theapparatus can be used to emulate an RF signal which an RF signaldetector would receive in a real environment in which there are a numberof RF sources. Accordingly, the apparatus can be used to train anoperator of the RF signal detector without the need for using real testRF sources. Furthermore, it can allow greater flexibility duringtraining, for example, by allowing the number, type and/orcharacteristics of the simulated (or “virtual”) RF sources to be easilycontrolled.

The apparatus may comprise a positioning device, such as a GPS receiver,for providing the location. The apparatus may comprise an interface forreceiving an indication of the location (for example, a selection madeusing a pointer on a map or a set of coordinates) and/or an instructionmodifying the location (for example, applying an offset). The interfacemay receive the indication from a remote location. The interface may bea user interface for receiving the indication or instruction locally.

The location of the apparatus may be used as the location of the RFsignal detector, the antenna associated with the RF signal detectorand/or the substitute device.

The at least one processor may be configured to calculate eachrespective weight in dependence upon location of a respective wirelessRF transmitter being simulated. The apparatus may comprise an interfacefor receiving an indication of the locations of the wireless RFtransmitter being simulated (for example, a selection made using apointer on a map or a set of coordinates) and/or an instructionmodifying the location of the wireless RF transmitters being simulated(for example, applying an offset). The interface may receive theindication from a remote location. The interface may be a user interfacefor receive the indication or instruction locally.

The at least one processor may be configured to calculate eachrespective weight in dependence upon orientation of the antenna. Theapparatus may comprise an input for receiving antenna orientation.

The location and/or orientation may be fed back to the device and the atleast one processor can generate new weights in dependence upon thelocation and/or orientation.

Thus, as an operator moves and/or re-orientates the antenna, the deviceresponds in real time.

The antenna may be a handheld antenna. The antenna is preferably adirectional antenna. The antenna may be associated with the RF signaldetector by virtue of being operatively connected to the RF signaldetector. Thus, even if the antenna provides a received RF signal, theRF signal detector need not use or may discard the received RF signal.The antenna may be associated with the RF signal detector by virtue ofbeing tethered to the RF signal detector. For example, a cable (e.g. aco-axial cable) may be replaced by an electrically-insulating lead (or“dummy lead”) or an in-line isolator. Thus, the antenna, even if it iscapable of providing an RF signal, need not provide the received RFsignal to the RF signal detector. The antenna may be a dummy antenna (or“substitute antenna” or “substitute device”). Thus, the dummy antennamay not even be capable of receiving and providing an RF signal to theRF signal detector. The dummy antenna may be handheld. The antenna,which may be a dummy antenna, may comprise an orientation determiningdevice, such as a gyroscope. Thus, the antenna or the dummy antenna maymimic a directional antenna.

The RF signal may lie in a range between 10 kHz (or less) to 100 GHz (ormore).

The wired connection may be a co-axial cable. The wired connection maybe RF over fiber.

The at least one processor may be configured to calculate a gain andselect a frequency band which results in an RF signal havingcharacteristics (such as power and frequency) simulating an aggregatedRF signal resulting from one or more typical, in-range RF sources.

An RF source may be a mobile communication device, such as smart phonesand feature phones. An RF source may be a wireless data modem, such thatused in IEEE 802.11 and other wireless local area networks, and inBluetooth and other wireless personal local area networks. An RF sourcemay be a mobile data modem, such as that used in GSM, EDGE, UMTS, HSPAand/or other mobile networks. An RF source may be a GPS jammer. An RFsource may be a communications system jammer. An RF source may be an AMor FM radio transmitter. An RF source may be an eavesdropping devicehaving a wireless transmitter.

An environment comprising a mixture of RF sources and/or which mayinclude one or more of the same type of RF source may be simulated. Thenumber, type, location and/or characteristics of RF sources may changeover time.

The RF source may be a reflector or scatterer. Thus, the RF signal beingsimulated may result from scattering of RF transmissions from a radartransmitter and so the RF source may be a target for radar detectionand/or other parts of the physical environment (i.e. clutter). Suchradars can be monostatic, bistatic or multistatic.

The at least one processor may be configured to generate a set of IQdata based on at least two sets of weighted IQ data by linearlycombining the at least two sets of weighted IQ data.

The at least one processor may be configured to calculate eachrespective weight.

A weight may be a real number. The at least one processor may beconfigured to multiply each value in the set of IQ data by therespective weight.

A weight may be a complex number. The at least one processor may beconfigured to multiply each IQ pair in the set of IQ data by therespective complex weight.

The apparatus may further comprise a positioning device for providing aposition (such as the position of the antenna of signal detector, whichcan be assumed in many cases to be the same as the signal detector andthe signal generator) and the at least one processor may be configuredto calculate each respective weight in dependence upon the position. Thepositioning device may be a global positioning system (GPS) device orother satellite- or ground-based navigation system device. Thepositioning device may be an inertial navigation system (INS) device.The positioning device may include a user interface which allows theoperator to manually enter or select a position (for example, in theform of coordinates). The positioning device may be an interface forreceiving, from a remote location, the position or data for enabling theposition to be determined (e.g. the data may be carried by one or moretiming beacons).

The apparatus may further comprise a first database storing datarelating to propagation models and terrain. The propagation models mayinclude one or more of, for example, a free space model, a groundreflection (two-ray) model, a knife-edge diffraction model, a Hatamodel, a Longley-Rice model, an Okumura model, statistical multi-pathmodels. The at least one processor may be configured to calculate eachrespective weight in dependence upon a propagation model and terrain.

The apparatus may further comprise a second database storing datarelating to antenna characteristics, such as, for example, gain of theantenna which is connected to the signal detector. The gain may dependon direction and frequency. The at least one processor may be configuredto calculate each respective weight in dependence upon said antennacharacteristics.

The apparatus may further comprise a third database storing datarelating to characteristics of a plurality of RF sources. The at leastone processor may be configured to calculate each respective weight independence upon characteristics of the respective RF source. Thecharacteristics may include a transmit power, an antenna gain and/orposition. A position and/or other characteristics may depend on time,i.e. the RF source may be mobile and may change over time.

The apparatus may comprise a synthesiser configured to generate a set of(un-weighted) IQ data. The IQ data may take the form of a time series ofI and Q data values. The at least one processor may be configured toreceive the set of IQ data from the synthesiser and to apply acorresponding weight. Additionally or alternatively, the apparatus maycomprise fourth database storing at least one set of IQ data. The IQdata may take the form of recorded IQ data. The at least one processormay be configured to retrieve the set of IQ data from the fourthdatabase and to apply a corresponding weight.

The circuit may comprise a pair of digital-to-analog converters (DAC).The DACs may be configured to receive the IQ data (i.e. digital samplesof I and Q components) and to output analog I and Q signals. The circuitmay comprise a modulator. The modulator may be configured to receive theanalog I and Q signals from the DACs and to modulate the RF carriersignal.

The set of IQ data may be a first set of IQ data and the circuit may bea first circuit which is configured to receive the first set of IQ data,a first gain and a first frequency band and to generate a first RFsignal in the first frequency band. The at least one processor may beconfigured to generate a second set of IQ data based on at least one setof weighted IQ data. The apparatus may further comprise a second,different circuit configured to receive the second set of IQ data, asecond gain and a second frequency band which is different to the firstfrequency band and to generate a second RF signal in the secondfrequency band. Thus, the apparatus may be able to generate RF signalsin different bands.

The apparatus may comprise more than two circuits, each circuitproviding a respective RF signal in a different frequency band. Thecircuits may be distinct or separate, but of the same type.

The apparatus may further comprise an RF signal combiner which isconfigured to receive first and second RF signals (or more than two RFsignals) and to combine the RF signals. Thus, the apparatus can be usedto provide a multi-band RF signal. The apparatus may comprise a port forsupplying the multi-band RF signal to a wired connection.

The apparatus may comprise a port (or ports) for supplying the RF signal(respective RF signals) to a wired connection. Thus, the apparatus canprovide single-band RF signals.

The apparatus may comprise an amplifier for amplifying the RF signal.

The apparatus may comprise an antenna for transmitting the RF signalwirelessly.

The apparatus may further comprise an input for receiving antennaorientation data. The antenna orientation data may include bearing (or“azimuth”) data, elevation (or “inclination”) data and/or rotation data.The at least one processor may be configured to calculate eachrespective weight in dependence upon the antenna orientation. Theapparatus may further comprise a device configured to provide theantenna orientation data which is attached to an antenna or an antennasubstitute.

The apparatus may further comprise an interface configured to receiveinstructions from a remote location for controlling operation of theapparatus. The interface may include a wireless data modem or mobilenetwork modem. The apparatus may comprise or may further comprise aninterface configured to provide information on performance, for example,of the operator.

The apparatus may further comprise an interface configured to provide areference sequence for supplying to a signal generator. The signalprocessor may be configured to generate the set of IQ data so as tosimulate a signal that would have been received from a virtual testtransmitter including a time delay corresponding to a distance betweenthe virtual test transmitter and the signal detector. Thus, theapparatus may be used for time difference on arrival (TDOA) training.

According to a second aspect of the present invention there is provideda system comprising the apparatus and a signal detector. The signaldetector may be in wired connection with the apparatus. A path betweenan RF signal output of the apparatus and an RF signal input of thesignal detector need not include a wireless section.

The system may further comprise an antenna. The antenna may be ahandheld antenna. The antenna is preferably a directional antenna. Theantenna may be operatively connected to the RF signal detector. Theantenna may be tethered to the RF signal detector. The antenna may be adummy. The antenna may comprise an orientation determining device, suchas a gyroscope.

The signal detector may comprise a spectrum analyser. The signaldetector may comprise a RF power detector or a tunable RF powerdetector. The signal detector may comprise an RF receiver. The signaldetector may comprise wideband RF detector. The signal detector maycomprise a radar receiver (i.e. for target detection). The signaldetector may comprise a radar warning receiver. The signal detector maycomprise signal recorder. The signal detector may comprise a digitisingreceiver.

The signal detector and apparatus may be comprised in a single unit.Thus, a signal detector may be provided with an in-built trainingmodule.

The signal detector may include an interface for receiving instructionfrom a remote location for controlling operation of the apparatus and/orsignal detector, and/or for transmitting information on performance.

The signal generator may include an interface configured to provide areference sequence for supplying to the signal detector and the signalprocessor is configured to generate the set of IQ data so as to simulatea signal that would have been received from a virtual test transmitterincluding a time delay corresponding to a distance between the virtualtest transmitter and the signal detector. The signal detector may beconfigured to carry out a correlation measurement for a time differenceon arrival (TDOA) measurement.

According to a third aspect of the present invention there is providedapparatus comprising a signal generating part which includes at leastone processor configured to generate a set of IQ data based on at leastone set of weighted IQ data, the or each set of weighted IQ data havinga respective weight and signal detecting part which includes at leastone processor configured to provide a signal to a user interface basedon the set of IQ data. The user interface may include a display.

Thus, weighted IQ data can be used to generate data for simulating arespective wireless RF transmitter without the need for generating an RFsignal.

According to a fourth aspect of the present invention there is provideda system comprising at least two apparatuses and at least two signaldetectors. Each signal detector may be in wired connection with arespective apparatus. Each apparatus may be configured to simulate thesame environment. For example, each apparatus may be provided with andprocess the same data but with different detector positions and sametransmitter positions. This can allow team training and permit, forexample, operators to cooperate and triangulate the position of avirtual RF source.

According to a fifth aspect of the present invention there is provided amethod comprising generating a set of IQ data based on at least one setof weighted IQ data, each set of weighted IQ data having a respectiveweight and generating an RF signal using the set of IQ data, andcalculating each respective weight in dependence upon location of an RFsignal detector or an antenna associated with the RF signal detector.The location may be an actual location or a simulated location.

The method may comprise calculating each respective weight in dependenceupon location of a respective wireless RF transmitter being simulated.

The method may further comprise calculating each respective weight.

According to a sixth aspect of the present invention there is provided acomputer program which, when executed by one or more processors, causesthe one or more processors to perform the method.

According to a seventh aspect of the present invention there is provideda non-transitory computer readable medium storing a computer programwhich, when executed by one or more processors, causes the one or moreprocessors to perform the method.

According to an eighth aspect of the present invention there is provideda hardware logic circuit configured to perform the method.

According to a ninth aspect of the present invention there is provided amethod of training an operator of a signal detector, the methodcomprising using a signal generator to provide a signal to the signaldetector which emulates an RF signal which the signal detector wouldreceive in a real environment comprising at least one real wireless RFsource. The signal generator is configured to generate the signal independence upon location of the signal detector, an antenna associatedwith the signal detector. The location may be an actual location or asimulated location. The location of the apparatus may be used as thelocation.

The method may comprise supplying a location of the signal detector tothe signal detector and/or supplying a location of each signal detectorto the signal detector.

Thus, a trainer can set or change the location of the detector and/ofthe sources to help test the operator.

The method may comprise supplying an orientation of an antenna to thesignal detector.

According to a tenth aspect of the present invention there is provided amethod of testing a signal detector, the method comprising using asignal generator to provide a signal to the signal detector whichemulates an RF signal which the signal detector would receive in a realenvironment comprising at least one real wireless RF source.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the present invention will now be described, byway of example, with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates training an operator of an RF signaldetector using remote RF sources which transmit wireless RF signals;

FIG. 2 schematically illustrates training an operator of a signaldetector using an RF signal generator which provides an RF signal to anRF signal detector via a wired connection;

FIG. 3 schematically illustrates virtual test transmitters simulatedusing the RF signal generator shown in FIG. 2;

FIG. 4 is a schematic block diagram of an RF signal generator;

FIG. 5 is a schematic block diagram of a transmitter section of the RFsignal generator shown in FIG. 4;

FIG. 6 a schematically illustrates training an operator of an RF signaldetector by an instructor using a remote station;

FIG. 7 is a process flow diagram of a process carried out by aprocessing section in the RF signal generator shown in FIG. 7;

FIG. 8 is a process flow diagram of a process of computing IQ data;

FIG. 9 schematically illustrates a RF signal generator receiving antennaorientation data;

FIG. 10 schematically illustrates a RF signal generator being used intime difference of arrival arrangement; and

FIG. 11 schematically illustrates exchanged of signals between detectorstations for a time difference of arrival measurement.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Referring to FIG. 1, a radio frequency (RF) signal detector 1 is shown.The RF signal detector 1 can take the form of spectrum analyser. The RFsignal detector 1 is coupled to an antenna 2 thereby allowing the RFsignal detector 1 to detect wireless RF signals.

As shown in FIG. 1, a user 3 (herein referred to as an “operator” or“trainee”) can be trained by an instructor (not shown) to use the signaldetector 1 by employing one or more test transmitters 4 which transmitrespective wireless RF signals 5 located in a surrounding area 6.

The area 6 may be an enclosed space, such as building, installation,vehicle or vessel, or part of a building, installation, vehicle orvessel. The area 6 may be semi-enclosed or bounded, such as a stadium orstreet. The area 6 may be open, such as open ground. The area 6 may bemixture of different types of spaces. The area 6 may include land and/orsea.

Referring to FIG. 2, a training system 7 is shown. The training system 7includes the signal detector 1 and an RF signal generator 8. An RFoutput 9 of the signal generator 8 is coupled to an RF input 10 of thesignal detector 1 via a wired connection ii (such as a co-axial cable)to supply an RF signal 12 directly to the signal detector 1.

The signal generator 8 does not need to transmit a wireless RF signal.Thus, the signal generator 8 may be one which is only capable oftransmitting low-power RF signals, for example, in a range of −150 dBmto +10 dBm. However, the signal generator 8 may be one which is capableof transmitting RF signals at a higher power, e.g. greater than +10 dBm.

As shown in FIG. 2, no wireless test transmitters 4 (FIG. 1) need beused.

Referring also to FIG. 3, the training system 7 can be used to providean apparent signal environment (or “simulated environment”) 13 whichincludes one or more simulated RF test transmitters 14 (herein referredto as “virtual test transmitters”) transmitting simulated wireless RFsignals 15.

The virtual test transmitters 14 do not physically exist. However, thesignal generator 8 imitates the signal environment that the virtual testtransmitters 14 would have produced at the RF input of the signaldetector 1 if they were real. Thus, the signal generator 8 can helpcircumvent the need for using real test transmitters 4 (FIG. 1).

Each virtual test transmitter 14 may be fixed or mobile. The signalgenerator 8 can mimic the signal environment as it would appear to thesignal detector 1 at a particular position, p_(d). The signal detectorposition may include latitude and longitude (or other set oftwo-dimensional coordinates) and, optionally, height.

As will be explained in more detail later, the signal generator 8 cansimulate changes in signal strength resulting from changes inorientation of a real, but non-operational directional antenna orsubstitute device 41 (FIG. 9). The signal generator 8 can play backpreviously recorded signals. The signal generator 8 can be controlledfrom a remote station 36 (FIG. 6) by an instructor 38 (FIG. 6) and sovary the signal environment presented to the operators 3.

The training system 7 may be used for training and/or assessingoperators 3 in techniques of signal detection, direction finding (or“transmitter geolocation”), signal identification and eavesdropping. Thesystem 7 can be used in-the-field, for example, in an area of the typein which the signal detector 1 would typically be used.

The signal generator 8 may be portable. However, the signal generator 8may be semi-portable (i.e. capable of being moved by, for example one ortwo persons, but is not intended for ready transportation) or mounted toa vehicle (such as a truck) or fixed platform. The sensing equipment 1may be portable, semi-portable, or mounted to a vehicle or fixedplatform.

The sensing equipment 1 need not be specially-adapted other than byreplacing a connection to the antenna 2 (FIG. 1) by the wired connectionii. Thus, the signal generator 8 can be used with an existing signaldetector 1, for example, detection equipment that a customer already hasin service.

Referring to FIG. 4, an example of a signal generator 8 is shown.

The signal generator 8 is able to produce signals corresponding to alarge number (e.g. hundreds) of virtual test transmitters 14 (FIG. 3),each having a respective position at a given time.

The signal generator 8 includes a signal processor 21, a weightcalculator 22, memory 23, one or more RF signal-generating circuits 24(herein referred to as “tuneable RF modulator sections”) and an RFsignal combiner 25. The signal processor 21 and a weight calculator 22are implemented in software running on one or more processors 26.

In some embodiments, the one or more processors 26 may include one ormore programmable central processing units capable of executing code toperform the functions and operations taught herein. In some embodiments,the one or more processors 26 may include one or more circuits orcircuitry, for example, field programmable gate arrays configurable orprogrammable to perform the functions and operations taught herein. Insome embodiments, the one or more processors 26 may include acombination of one or more programmable central processing units and oneor more configurable circuits or circuitry to perform the functions andoperations taught herein.

The signal generator 8 includes first and second sources 27, 28 ofdigital in-phase (I) and quadrature (Q) data (herein referred to simplyas “IQ data”) which are used to generate signals corresponding to thevirtual test transmitters 14 (FIG. 3).

The first IQ data source 27 takes the form of a synthesiser whichcalculates and outputs an IQ time series of I and Q data pairs for agiven virtual test transmitter 14 (FIG. 3). The synthesiser 27 may beimplemented in software running on the one or more processors 26.

The second IQ data source 28 takes the form of a database 23 (hereinreferred to an “IQ data source database”) which stores pre-recorded IQdata. The IQ data can be obtained using an RF signal detector bydemodulating a received RF signal to produce analog I and Q components,digitising the analog I and Q components to produce digital I and Q datastreams and storing the I and Q data streams. Pre-recorded IQ data maycorrespond to a single virtual test transmitter 14 (FIG. 3). However,pre-recorded IQ data may correspond to more than one virtual testtransmitter 14 (FIG. 3). A recording of RF signals from, say, a distantcity or other site having multiple RF sources can be used.

Referring still to FIG. 4, the signal generator 8 includes additionaldatabases 29, 30, 31 and a positioning device 32. A propagation modeland terrain database 29 stores data relating to propagation models andterrain. An antenna characteristics database 30 stores data relating tocharacteristics of the signal detector antenna 2 (FIG. 1). A virtualtest transmitter database 31 stores data regarding the virtual testtransmitters 14 (FIG. 3) including transmit power, antenna gain and(time-dependent) position. The databases 22, 29, 39 31 may be stored onone or more hard disk drives and/or solid-state hard drives (not shown).

The positioning device 32 is used to provide the position of the signaldetector 1. The positioning device 32 takes the form of a globalpositioning system (GPS) receiver. Additionally or alternatively, aninertial navigation system may be used. The position may be enteredmanually via a user interface (not shown).

Based on data taken from the databases 29, 30, 31 and the signaldetector position, the weight calculator 22 calculates a weight w,typically a real number, for each selected virtual test transmitter 14(FIG. 3) and supplies the weights w to the signal processor 21.

The signal processor 21 applies the weight w (by multiplication) to aset of synthesised or pre-recorded IQ data to generate a set of weightedIQ data.

The signal processor 21 linearly combines one or more sets of weightedIQ data to form a set of IQ data for a tuneable RF modulator section 24.As will be explained in more detail later, different IQ data can beprovided to different tuneable RF modulator sections 24.

Referring also to FIG. 5, each tuneable RF modulator section 24 includesa pair of digital-to-analog converters (DAC) 33 and a tuneable RFsection 34. The signal processor 21 supplies IQ data to the DACs 33 forconversion into corresponding analog I and Q signals. The signalprocessor 36 also supplies a gain value and frequency band informationto the tuneable RF section 34. Frequency bands having the same ordifferent widths can be used.

The tuneable RF section 34 modulates a carrier frequency to produce anintermediate frequency (IF) signal. The tuneable RF section 34 mayinclude a frequency conversion section which may include one or moreup-conversion and/or down-conversion paths. A path can be chosen toselect the required frequency band.

Other forms of tuneable RF modulator section 24 may be used. Forexample, modulation can be performed in the digital domain and theresulting digital data stream is converted by a single DAC into ananalogue signal. The analogue signal can then be up-converted ordown-converted as necessary.

The signal generator 8 can replicate virtual transmitter characteristics(such as modulation waveform, etc.), although this may be limited by thebandwidth and dynamic range of the tuneable RF modulator sections 24.

A scenario, i.e. positions as a function of time and signalcharacteristics of virtual transmitters 14 (FIG. 3), may bepre-programmed (stored in the virtual transmitter database 31). However,the scenario may be controlled from a remote station.

Referring to FIG. 6, an instructor-controlled training system is shown.The system includes the signal detector 1 and signal generator 6provided with a communications network interface 35 and a remote station36 provided with a communications network interface 37. Thecommunications network may wireless or wired. The remote station 36 maytake the form of a personal computer. The remote station 38 might beused, for example, by an instructor 38 to create dynamic, time-varyingsignal detection problems for a trainee (i.e. operator 3) bytransmitting instructions 39 for controlling the signal generator 8 andto receive telemetric information 40 on his or her performance. This caninclude setting or adjusting the location of the signal detector 1and/or the location(s) of the virtual transmitter(s).

Referring to FIGS. 4 to 8, operation of the signal generator 8 will befurther described in more detail.

When operation starts, a stream of synthesised or pre-recorded IQ databegins to be buffered in memory 23 (step S1).

The signal processor 21 initialises a tuneable RF modulator sectioncounter, j (step S2).

Taking IQ data from memory 23, the signal processor 21 calculates IQdata in a first time window for a first tuneable RF modulator section 24(step S3) and outputs a stream of IQ data, a gain value and frequencyband information to the first tuneable RF modulator section 24 (steps S4& S5).

In step S3, the signal processor 21 identifies the virtual testtransmitters 14 (FIG. 3) which need to be considered for the current(j-th) section 24 and determines their number, N_(j) (step S3.1). Thisis to take into account the fact that certain virtual test transmitters14 (FIG. 3) may not contribute to the current frequency band. Forexample, one of the two GPS carrier frequencies may fall into thefrequency range of the current tuneable RF modulator section 24 and sovirtual test transmitters 14 (FIG. 3) which are not a source or asignificant source of RF power in this frequency band can be ignored,while other sources (such as a GPS jammers) are included and counted.

The signal processor 21 initialises a virtual test transmitter counter i(step S3.2) and clears a section of memory 23 reserved for storing awindowed stream of accumulated weighted IQ data, i.e. to form a windowedstream of linearly-combined IQ data (step S3.3).

The weight calculator 22 retrieves the characteristics for the current(i.e. i-th) virtual transmitter 24 and other data from databases 29, 30,31 (step S3.4). Using this data and the current position, the weightcalculator 22 calculates the weight w for the current virtualtransmitter and passes this to the signal processor 21 (step S3.5).

The signal processor 21 retrieves a windowed stream of synthesised orpre-recorded IQ data from (a different section of) memory 23, appliesthe calculated weight to each IQ data value (step S3.6) and adds thiswindowed stream of weighted IQ data to the section of memory 23 reservedfor storing accumulated weighted IQ data (step S3.7).

The signal processor 21 increments the virtual test transmitter counteri (step S3.8) and repeats steps S3.4 to S3.7 for the virtual testtransmitter counter 24 until all relevant virtual test transmitters havecontributed to accumulated weighted IQ data (step S3.9).

The signal processor 21 then reads out the accumulated weighted IQ data(i.e. linearly-combined IQ data) as a stream of IQ data to the currenttuneable RF modulator section 24 (step S3.10).

The signal processor 21 increments the tuneable RF modulator sectioncounter j (step S6) and repeats steps S3 to S5 for the next tuneable RFmodulator section 24 in the same time window until respective IQ data,gain values and frequency band information have been provided to all thetuneable RF modulator sections 24 (step S7).

Thus, each tuneable RF modulator section 24 generates a (single-band) RFsignal in a time window. The combiner 25 add these signals to form the(multi-band) output RF signal 12 which is presented to the RF outputport 9.

Using a directional antenna can help identify and locate an RF source.Accordingly, the signal generator 8 can be adapted to take into accountorientation of a directional antenna. Thus, training indirection-finding (DF) techniques can be provided using the signalgenerator 8. For example, the operator must determine a signal directionby finding the direction of strongest signal.

Referring to FIG. 9, an arrangement is shown which includes adirectional antenna (or a substitute device) 41 and a sensing device 42attached to the antenna 41 capable of measuring instantaneous angle(s)of orientation of the antenna 41 and outputting antenna orientation data43. The sensing device 42 may include MEMS-type accelerometers and/or amagnetic compass. If an antenna is used (i.e. a substitute device is notused), then no RF signal is taken from the antenna.

The antenna orientation data 43 includes an azimuthal angle (or“bearing”). The antenna orientation data 43 may include an angle ofelevation. This can be used to train the operator to find an elevated(or lowered) or airborne RF sources. The antenna orientation data 43 mayinclude axial rotation. This can be used to train the operator toidentify polarized sources.

As shown in FIG. 9, the signal generator 8 receives the antennaorientation data 43 via input 44. The weight calculator 22 (FIG. 4)takes into account the antenna orientation data when calculatingweights. In particular, weight calculator 22 (FIG. 4) uses the antennaorientation data together with antenna gain characteristics stored inthe antenna characteristics database 30 (FIG. 4).

Thus, the signal generator 8 can mimic the effect on the strengths ofthe signals received from virtual transmitters that would have beenproduced by the actual directional antenna gain at the measuredorientation of the device. The operator can respond to the signalindicated by the signal detector 1 by moving the directional antenna 41.

The antenna or substitute device 41 may be handheld. However, theantenna need not be handheld but can be any form of rotatabledirectional antenna, for example, mounted on a vehicle or fixedplatform.

Information relating to movement of the signal detector 1 and/or antenna41 over time can be recorded and may be stored in the signal generator 8and/or transmitted via a wireless data interface (not shown) to a remotestation, e.g. for use by an instructor.

As shown in FIG. 2, a single signal detector 1 can be used inconjunction with a single signal generator 8. However, the system mayinclude more than one signal detector 1 and a corresponding number ofsignal generators 8 that are synchronised and so present signals fromthe same set of virtual transmitters to each signal detector 1.

This can be used for team training, where members of a team co-operateto detect and identify multiple virtual signals.

Techniques used by teams include carrying out angle of arrival (AOA)direction-finding measurements from multiple locations to triangulate atransmitter location.

Signal detectors 1 and signal generators 8 may also be used for trainingoperators at a control centre (not shown). Pairs of signal detectordetectors 1 and signal generators 8 may report measurements to a remotecontrol centre and the operators at the control centre (not shown) caninterpret the measurements.

Another technique, used by individuals or teams, is proximity detectionusing power on arrival (POA). This technique is particularly useful whenused in confined space, such as a building. In this technique, an RFsource is located by approaching it closely enough to maximise powerreceived.

It is also possible for members of a team, who are able to communicatewith each other, to be trained in time difference of arrival (TDOA)transmitter location, using signal generators 8.

To make TDOA measurements, a signal detector 1 needs an IQ referencesequence, for example, in the form of sampled time series, as the basisfor correlation with the received signal. In existing systems, suchreference sequences are sent over wireless broadband communicationslinks. However, in the present system, reference sequences can be sentfrom the signal generators 8, which already has IQ sequence informationfor the virtual transmitter, to the signal detector 1.

Referring to FIG. 10, a TDOA arrangement is shown.

Correlation measurement data 51 are exchanged with other team membersvia a communications antenna 52 and a low-bandwidth (i.e. not broadband)data communications interface 53 in the signal detector 1.

The signal generator 8 includes a data communications interface 54 and awired connection 55 to provide the reference sequences 56 using, forexample, short-range Ethernet.

Referring also to FIG. 3, the signal generator 8 sends an RF signal 12to the signal detector 1, simulating the signal that would have beenreceived from a virtual test transmitter 14 including the relevant timedelay corresponding to the distance between the virtual test transmitter14 and the signal detector 1.

Referring also to FIG. 11, correlation measurements made at various (atleast three) detector stations 61 are shared between team members overlow data rate wireless communications links, as are the locations of thedetector stations 61. A TDOA location estimation calculation may then beperformed at any of the detector stations that has received a full setof correlation results and associated detector locations. The behaviourof the signal generators can be synchronised using GPS.

Thus, using signal generators 8 can help to reduce greatly the wirelessbandwidth required for transmission between detector stations.

As explained earlier, the signal generator 8 may be incorporated into asignal detector 1 to form a single unit (not shown). Thus, an operatormay switch the signal detector 1 into “simulation mode” in which theunit is programmed to output pre-defined signals.

The signal generator portion of the unit may provide an RF signal to thesignal detector portion of the unit in the analog domain.

Alternatively, the signal generator portion of the unit may providedigital signals to the signal detector portion of the unit in thedigital domain. In this case, digital signals can be “injected” into adigital path near the detector output (such as a processor input, priorto the data or representation of the data being displayed).

A further use of signal injection in the digital domain is thesimulation of TDOA measurements. Signals can be injected into a centralcalculation point for transmitter location estimation.

All the techniques hereinbefore described may be combined in a singletraining or assessment exercise, to include multiple in-fieldindividuals and controllers at a central point, all overseen by aninstructor who can determine the signal scenarios presented to thetrainees, and measure their performance.

The examples hereinbefore described use wired connections to avoid theneed for wireless RF test transmitters 4 (FIG. 1).

However, the RF signal 12 (FIG. 2) can be wirelessly transmitted fromthe signal generator 8 (FIG. 2) using an antenna (not shown).

A signal generator 8 which wirelessly transmits an RF signal (FIG. 2)may also serve as a geo-location beacon for use by receivers when GPS isnot available.

For example, wireless transmission of an RF signal (FIG. 2) from asignal generator 8 can be used to synchronise a network of signaldetectors 1, such as RFeye® nodes, by providing a timing beacon in theabsence of effective GPS signals.

Wireless transmission of an RF signal (FIG. 2) from a signal generator 8can be used for tracking of assets, such as vehicles, by placing asignal generator 8 on each asset. Surrounding receiver, such as RFeye®nodes, can locate the asset using direction-finding techniques.

It will be appreciated that many modifications may be made to theembodiments hereinbefore described.

For example, the signal detector may be a digital or analog detector.The signal detector may include a display for displaying a signal.

The signal generator can be used be to test signal detecting equipment.

1. Apparatus comprising: a positioning device for providing a locationof an RF signal detector or a location of an antenna associated with theRF signal detector; an orientation determining device for providing anorientation of the antenna associated with the RF signal detector; atleast one processor configured to generate a set of IQ data based on atleast one set of weighted IQ data, each set of weighted IQ data having arespective weight; and a circuit configured to generate an RF signalusing the set of IQ data; wherein the at least one processor isconfigured to calculate each respective weight in dependence upon thelocation and the orientation.
 2. (canceled)
 3. Apparatus according toclaim 1, further comprising: an interface for receiving an instructionmodifying the location.
 4. (canceled)
 5. Apparatus according to claim 1,wherein the at least one processor is configured to calculate eachrespective weight in dependence upon location of a respective wirelessRF transmitter being simulated.
 6. Apparatus according to claim 1,wherein the at least one processor is configured to calculate eachrespective weight in dependence upon orientation of the antenna. 7.(canceled)
 8. Apparatus according to claim 1, wherein the antenna is ahandheld antenna.
 9. Apparatus according to claim 1, wherein the antennacomprises an orientation determining device.
 10. Apparatus according toclaim 1, wherein the antenna is a dummy antenna.
 11. Apparatus accordingto claim 1, wherein the at least one processor is configured to generatea set of IQ data based on at least two sets of weighted IQ data bylinearly combining the at least two sets of weighted IQ data. 12.(canceled)
 13. Apparatus according to claim 1, further comprising: afirst database storing data relating to propagation models and terrain;wherein the at least one processor is configured to calculate eachrespective weight in dependence upon a propagation model and terrain.14. Apparatus according to claim 1, further comprising: a seconddatabase storing data relating to antenna characteristics of a givensignal detector; wherein the at least one processor is configured tocalculate each respective weight in dependence upon said antennacharacteristics.
 15. Apparatus according to claim 1, further comprising:a third database storing data relating to characteristics of a pluralityof RF transmitters; wherein the at least one processor is configured tocalculate each respective weight in dependence upon characteristics ofthe respective RF transmitter.
 16. Apparatus according to claim 15,wherein the characteristics include a transmit power. 17-18. (canceled)19. Apparatus according to claim 16, wherein the position depends ontime.
 20. Apparatus according to claim 1, further comprising: asynthesiser configured to generate a set of IQ data; wherein the atleast one processor is configured to receive the set of IQ data from thesynthesiser and to apply a corresponding weight.
 21. Apparatus accordingto claim 1, further comprising: a fourth database storing at least oneset of IQ data; wherein the at least one processor is configured toretrieve the set of IQ data from the fourth database and to apply acorresponding weight.
 22. Apparatus according to claim 1, wherein thecircuit comprises: a pair of DACs; wherein the DACs are configured toreceive the IQ data and to output analog I and Q signals.
 23. Apparatusaccording to claim 1, wherein the circuit comprises: a modulator;wherein the modulator is configured to receive the analog IQ signalsfrom DACs and to modulate the RF carrier signal to provide anintermediate signal.
 24. Apparatus according to claim 1, wherein thecircuit comprises: a set of at least one up-converter and/ordown-converter, one of which is selectable so as to allow up-conversionor down-conversion of the intermediate signal.
 25. Apparatus accordingto claim 1: wherein the set of IQ data is a first set of IQ data, thecircuit is a first circuit which is configured to receive the first setof IQ data, a first gain and a first frequency band and to generate afirst RF signal in the first frequency band, and wherein the at leastone processor configured to generate second set of IQ data based on atleast one set of weighted IQ data: a second circuit configured toreceive the second set of IQ data, a second gain and a second frequencyband which is different to the first frequency band and to generate asecond RF signal in the second frequency band.
 26. Apparatus accordingto claim 25, further comprising: an RF signal combiner; wherein thecombiner is configured to receive first and second RF signals and tocombine the signals to provide a multi-band RF signal.
 27. Apparatusaccording to claim 26, further comprising: a port for supplying themulti-band RF signal to a wired connection.
 28. Apparatus according toclaim 1, further comprising: a port for supplying the RF signal to awired connection.
 29. (canceled)
 30. Apparatus according to claim 1,further comprising: an interface configured to receive instructions froma remote location for controlling operation of the apparatus. 31.Apparatus according to claim 1, further comprising: an interfaceconfigured to provide information on performance.
 32. Apparatusaccording to claim 1, further comprising: an interface configured toprovide a reference sequence for supplying to a signal detector; and thesignal processor is configured to generate the set of IQ data so as tosimulate a signal that would have been received from a virtual testtransmitter including a time delay corresponding to a distance betweenthe virtual test transmitter and the signal detector.
 33. A systemcomprising: apparatus according to claim 1; and a signal detector;wherein the signal detector is in wired connection with the apparatus.34. A system according to claim 33, wherein the signal detectorcomprises a spectrum analyser.
 35. A system according to claim 33,wherein the signal detector and apparatus are comprised in a singleunit.
 36. A system according to claim 33, wherein the signal detectorincludes an interface for receiving instruction from a remote locationfor controlling operation of the apparatus and/or signal detector,and/or for transmitting information on performance.
 37. A systemcomprising: at least two apparatuses according to claim 11; and at leasttwo signal detectors; wherein each signal detector is in wiredconnection with a respective apparatus, wherein each apparatus isconfigured to simulate the same environment. 38-45. (canceled)